我们应该手动设置$ _SERVER ['REQUEST_URI']吗？

Should we manually set $_SERVER['REQUEST_URI'] or will the server itself provide it?

Because I am not able to get it in my code,

$Gpath = explode('/login.php', $_SERVER['REQUEST_URI']);

Nope, we shouldn't. It's set by the server.

Your code makes not much sense though.
You'd better tell us what it's intended for, so we can tell you a proper way

No you should not manually set it. It is a predefined variable.

If you're planning to deploy on Linux/Unix system, this variable will in all likelyhood be correctly set, so you should simply use it as-is.

However, as you're developing on Windows XP, you may need to fake it with a script along the lines of:

// Fake REQUEST_URI on Windows.
if(!isset($_SERVER['REQUEST_URI']) && strtoupper(substr(PHP_OS, 0, 3) == 'WIN')) {
    $_SERVER['REQUEST_URI'] = $_SERVER['SCRIPT_NAME'];
    if($_SERVER['QUERY_STRING']) {
        $_SERVER['REQUEST_URI'] .= '?' . $_SERVER['QUERY_STRING'];
    }
}

N.B.: I'm not running on Windows, so can't test this, but you should be able to cobble something together along these lines. (If you do a print_r($_SERVER), you can see what's available.)